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BMSC > Spermatogenesis > Flashcards

Spermatogenesis Flashcards

1
Q

Where do spermatazoa develop?

A

In the seminiferous tubules of the testis

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2
Q

What cells help the development of spermatazoa?

A

Sertoli cells

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3
Q

Where in the testis are androgens synthesised?

A

Between the seminiferous tubules

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4
Q

What cells synthesize androgens in the testis?

A

Leydig cells

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5
Q

What are the two functions of the blood testis barrier?

A
  1. Prevent intratubular sperm from leaking out and causing the production of anti sperm antibodies.
  2. To maintain the difference in composition between intra and extra tubular fluids. This allows the later stages of spermatogenesis to occur in a controlled chemical microenvironment.
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6
Q

Where does the proliferative stage of spermatogenesis occur?

A

In the basal intratubular compartment of the testis

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7
Q

What type of junctions are formed between sertoli cells and what is the function of these?

A

Tight Junctions. Function is to create a blood testis barrier which prevents an immune reaction to sperm and allows a distinct environment in the testis.

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8
Q

What is the approximate length of spermatogenesis?

A

64 days

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9
Q

What two stages can spermatogenesis be subdivided into?

A
  1. Spermatocytogenesis
    (Spermatogonium up to secondary spermatocyte)
  2. Spermiogenesis (Differentiation/Maturation of the sperm cell)
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10
Q

Describe the mitotic proliferation of spermatogonia is the first stage of spermatogenesis?

A

Cells are resting at interphase before puberty when mitosis restarts. There are different types of cells which emerge and some divide by mitosis to maintain the spermatogonia population.

  1. The beginning of spermatogenesis is marked by the presence of A1 spermatogonia which remain bound together by thin bridges of cytoplasm. It is the preservation of these cytoplasmic connections that induce spermatogonia into the spermatogenesis process
  2. After a further mitotic division type B spermatogonia are produced that divide mitotically into primary spermatocytes.
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11
Q

Where does the mitotic proliferation of spermatogeneisis occur?

A

In the basal compartment of the seminiferous tubules

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12
Q

Are primary spermatocytes diploid or haploid cells?

A

Diploid

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13
Q

Where do the primary spermatocytes go to duplicate their DNA?

A

Adluminal compartment of the seminiferous tubules

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14
Q

At what stage do the primary spermatocytes enter meiosis 1 and what happens?

A

S phase and double their internal DNA.

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15
Q

What are the five stages of the prophase of meiosis 1?

A 
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis.
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16
Q

What happens in the S stage of the cell cycle?

A

The DNA of each chromosome is replicated so that is consists of two identical sister chromatids, which are still held together

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17
Q

What happens after the S phase (DNA replication) in meiosis?

A

Cells enter meiotic prophase:
1. Homologous chromosomes pair with each other and undergo genetic recombination
2.

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18
Q

Why does the ploidy of the cell not change in meiosis when the chromosomes duplicate?

A

The centromere number remains the same

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19
Q

What are the four main stages of meiosis?

A

Prophase
Metaphase
Anaphase
Telophase

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20
Q

Give 2 ways in which meiosis generates genetic diversity?

A
  1. The independant orientation of homologous chromosome pairs along the metaphase plate during metaphase 1 and the subsequent separation of homologs during anaphase 1 allows a random distribution of chromosomes amongst daughter cells.
  2. Physical exchange of homologous chromosomal regions by recombination during prophase 1 results in new combinations of DNA within chromosomes.
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21
Q

What is the longest phase of meiosis?

A

Prophase 1

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22
Q

What happens in prophase 1?

A
  1. Leptotene
    - Individual chromosomes (consisting of 2 chromatids) become individualised to form visible strands within the nucleus. At this stage the synpatonemal complex forms which mediates pairing, synapsis and recombination
  2. Zygotene
    - Chromosomes like up with each other into homologous chromosome pairs
  3. Pachytene
    - A tetrad of the chromosomes has formed known as a bivalent. Chromosomal crossover occurs. At sites where this exchange happens chiasmata form.
  4. Diplotene
    - The synaptonemal complex degrades and homologous chromosomes separate from each other.
  5. Diakinesis
    - Chromosomes condense further.
    - Nucleoli disappear, nuclear membrane disintegrates into vesicles and the meiotic spindle begins to form.
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23
Q

What happens in metaphase 1?

A

Spindle fibres attach to chromosomes and chromosomes line up in the centre of the cell with their homologous pair

24
Q

At what stage of meiosis do the two centrosomes migrate to the two poles of the cell?

A

During prophase.

25
Q

What protein complex holds sister chromatids together from replication until anaphase?

A

Cohesin

26
Q

What happens in anaphase 1?

A

Homologous chromosomes (consisting of a pair of sister chromatids) are pulled to opposite poles of the cell.

27
Q

Why are sister chromatids able to stay together during anaphase 1?

A

The cohesin surrounding the centromere is protected which means sister chromatids stay together while homologous chromosomes are separated

28
Q

When does the first meiotic divison end?

A

When the chromosomes arrive at the opposite poles.

29
Q

In telophase 1 how many chromosomes and chromatids does each new cell have?

A

23 chromosomes each consisting of two sister chromatids

30
Q

What happens in telophase 1?

A

Microptubules that make up the spindle network disappear and a new nuclear membrane surrounds each haploid set of chromosomes. Cytokinesis then occurs completing the creation of two daughter cells. Cells then enter a period of rest known as interphase 2 when no DNA replication occurs.

31
Q

What is meiosis 2?

A

Second meiotic division that involves the separation of sister chromatids and results in the creation of 4 haploid cells.

32
Q

Describe the stages of meiosis 2?

A

Prophase 2: Disappearance of the nucleoli and nuclear envelope as well as shortening and thickening of the chromatids. Centrsomes move to the polar regions and arrange spindle fibres ready for the second division.
Metaphase 2: Chromosomes alighn randomly at the cells equator. The new equatorial plate is at 90 degrees when compared to that of metaphase 1.
Anaphase 2: Sister chromatids are separated (They are now called sister chromosomes as the move towards opposite poles
Telophase 2: Decondensation and lengthening of the chromosomes and the disassembly of the spindle. Nuclear envelopes reform and cleavage occurs producing 4 haploid cells.

33
Q

Whereabouts in the sperm do the mitochondria lie?

A

Midpiece

34
Q

What links the midpiece and the head of sperm?

A

Centrioles

35
Q

What part of the round spermatid cell later becomes the acrosome cap?

A

Golgi apparatus

36
Q

What four important processes occur in spermiogenesis?

A
  1. Nuclear condensation
  2. Acrosome formation
  3. Flagellum formation
  4. Cytoplasma reduction
37
Q

How is the acrosome formed?

A

The golgi apparatus engenders the vesicles which then merges into a larger formation that settles close to the cell nucleus and finally inverts itself like a cap over the largest part of the nucleus. The acrosome in functionally like a lysosome and contains lysosomal enzymes such as hyaluronidase.

38
Q

Where does the axonemal structure of the flagellum arise from?

A

Grows out of the distal centriole.

39
Q

Describe the four parts of the mature sperm flagellum?

A

Neck (contains the two centrioles)
Midpiece (contains a sheath of mitochondria grouped around the axoneme)
Principal piece (contains a sheath of ring fibres around the axoneme)
Tail (consists of only the 9 + 2 structure of the axoneme)

40
Q

How is the cytoplasm of the spermatids that is no longer needed disposed of?

A

Phagocytized by sertoli cells.

41
Q

What is the sperm axoneme and how does this enable sperm to move?

A

Structure composed of a characteristic 9 + 2 array of microtubules. This means that there are 9 outer microtubule doublets and 2 inner/central single microtubules.

42
Q

Describe how the sperm tail moves

A

Dyenin arms are one of the protein complexes found around the microtubules. Each dyenin arm in anchored to a doublet microtubule and by walking along an adjacent microtubule the dynein motors can cause the microtubules to slide against each other. When this happens in a synchronised fashion with microtubules on one side being pulled up and those on the other side being pulled down the axoneme as a whole cane bend back and forth. This causes flagellar beating.

43
Q

What protein makes up microtubules?

A

Tubulin

44
Q

what two subunits does a microtubule doublet in the sperm consist of? Which ones of these does dyenin attach to?

A

A and B subunits. Dyenin arms attach to the A subunit.

45
Q

What does dyenin do?

A

Translates chemical energy into kinetic energy by allowing adjacent microtubule doublets to slide relative to one another causing axonemal bending and flagellar movement.

46
Q

What hormone causes the leydig cells to release testosterone?

A

LH

47
Q

What cell does FSH act on? What does it cause in these cells?

A

Sertoli cells. Triggers the formation of testosterone binding protein meaning that testosterone can be transported by sertoli cells into the luminal compartment.

48
Q

When does the blood testis barrier arise?

A

Absent prepubertally but develops prior to the start of spermatogenesis

49
Q

Describe the mitotic proliferation seen in spermatogenesis.

A
  1. Quiescent interphase is reactivated at some uncertain point to re enter mitosis in the basal compartment of the tubule. They are now now know as spermatogonial stem cells.
  2. From within this resevoir some cells emerge which show a distinct morphology and these are called type A spermatogonia. The emergence of these cells marks the start of spermatogenesis.
  3. Each of these type A cells undergo mitotic divisions to produce 16 cells.
  4. These cells then undergo mitotic divisons resulting in type B cells which thenn divide to form resting primary spermatocytes
50
Q

What happens to the centriole in spermiogenesis?

A

They reduce to a central core structure linking the mid piece to the sperm head. They lose almost all of the pericentriolar material. (The opposite happens in the oocyte in which pericentriolar material is retained but centrioles are lost)

51
Q

What does the flagella grow from?

A

The distal centriole

52
Q

What forms the neck of the sperm?

A

Proximal centriole

53
Q

How is DNA condensation of sperm achieved?

A

Replacement of the histones by protamines causes tightly compressed chromatin in which genetic expression is absent.

54
Q

Discuss the genetic activity during spermatogenesis eg transcription of DNA.

A
  1. mRNA production and translation continue during mitosis and meiosis (NOT on the sex chromosomes)
  2. Autosomal transcription ceases during the transition from round to elongated spermatids)
55
Q

Which part of the epididymis absorbs around 90% of the fluid carrying the spermatazoa?

A

The vasa efferentia ( Initial segment of the epididymis)

56
Q

What hormone is vital for the absorption of fluid carrying spermatazoa?

A

Oestrogen

57
Q

What cells synthesize oestrogen in the testis?

A

Leydig cells

BMSC (17 decks)

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